Fuse device with overload means



Nov. 15, 1966 T. PLATZ FUSE DEVICE WITH OVERLOAD MEANS Filed Sept. 22, 1964 e o w u l n sus vu zobbuauv a a u .um

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United States Patent O 3,286,060 FUSE DEVICE WITH OVERLOAD MEANS Elwood T. Platz, Grosse Pointe Farms, Mich., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Sept. 22, 1964, Ser. No. 398,186 8 Claims. (Cl. 200-116) This invention relates to fuse devices in general and more particularly to a device having a fusible element and an overload means including a latch released in response to predetermined overload conditions below the level necessary to rupture the fusible element.

A device of this type is illustrated in U.S. Patent 2,982,834, issued May 2, 1961, to W. H, Edmunds for a Dual Element Fuse Device, and assigned to the assignee of the instant invention. In the device of the aforesaid patent there is a fusible element which ruptures on high short circuit currents to interrupt the circuit, while under lower predetermined overload conditions an auxiliary overload device responsive to heat developed in the fusible element operates a latch means to release a member which eventually serves to operate a series connected circuit interrupter.

More particularly, in the device of the aforesaid patent a bimetal strip mounted in close proximity to a fusible element and in a common housing therewith acts to latch a releasable member in an operative position. Upon suflicient heat being developed in the fusible member the bimetal strip deiiects to release the releasable member which is then free to move under the influence of a biasing spring into engagement with the trip mechanism of a series connected circuit breaker to cause opening thereof.

The device of the instant invention constitutes an irnprovement over the device of the aforesaid Patent 2,982,834 in that the bimetal strip is replaced by a spiraled bimetal with the latter being operable to rotate a latch sleeve causing the release of a trip bar when there is sufcient rotation of the latch sleeve. As will hereinafter become apparent, the utilization of .a spiraled rather than la strip biinetal results in fan extremely compact and rugged construction in which the tripping point for the overload device may readily be adjusted over a wide range.

Accordingly, a primary object ,of the instant invention is to provide a novel construction for a dual element fuse device.

Another object of this invention is to provide a novel compact fuse device for initiating overload operation without destroying the fusible element of the device.

Still another object of this invention is to provide a novel compact fuse device for initiating overload operation without necessitating fuse replacement.

These as well as other objects of this invention shall become readily apparent after reading the following description of the accompanying drawings in which FIGURE 1 is a side elevation of a fuse device constructed in accordance with the teachings of the instant invention.

FIGURE 2 is a cross-section taken through line 2-2 of FIGURE 1 looking in the direction of arrows 2-2.

FIGURES 3 and 4 are end views of the fuse device looking in the directions of arrows 3-3 and 4-4 of FIG- URE 2.

FIGURE 5 is across-section taken through line 5-5 of FIGURE 2.

FIGURE 6 is an end view of the latch sleeve.

FIGURE 7 is a cross-section taken through line 7-7 of FIGURE 6 looking in the direction of arrows 7-7.

FIGURE 8 is an end view of a modified latch sleeve construction.

Now referring to the figures. Fuse device 10 is pro- ICC vided with insulating hollow cylindrical housing 11 capped by ferrules 12 and 13 constituting terminals for the device. Disposed within housing 11 and positioned coaxial therewith is cylindrical fusible element 14 whose ends are outwardly flared with radially extending end portions welded or otherwise secured to the inside surfaces of ferrules 12 and 13. Ring locating means 15 is secured to the inside surface of ferrule 12 and is positioned concentric with cylindrical housing 11. Insulating cylindrical tubular member 16 positioned adjacent the inner surface of fusible element 14 is retained at one end by ring 15 and at the other end is press fitted in a central opening of ferrule 12.

Disposed Within insulating tube 16 are sleeve 21, spiraled bimetal 22, coil spring 23, latch sleeve 24, trip bar 25 and insulating hollow cylindrical spacer 26. One end of bimetal 22 is welded or otherwise secured at 31 to one end of sleeve 21 whose other end 32 is deformed and extends through slot 33 in ferrule 13 for a reason to be hereinafter explained. The other end of bimetal 22 is secured to one end of latch sleeve 24 whose other end abuts one end of spacer 26. The axial extension 36 of calibrating bushing 35 extends into tube 16 and abuts the other end of spacer 26.

Trip member 25 is an elongated element of generally rectangular cross section having an enlarged central portion 25a and portions 25b, 25e at opposite ends of enlarged portion 25a. Spring 23 surrounds trip member portion 25e with one end of spring 23 abutting the right end (with respect to FIGURE 2) of member 21 and the left end of spring 23 abutting the right end of enlarged portion 25a. Enlarged portion 25a is for the most part surrounded by latch sleeve 24.

Under normal operating conditions trip member 25 is restrained in the position illustrated in FIGURE 2 with the left end of enlarged portion 25a abutting the inner surface of latch sleeve 24 at the left end 24a thereof. As seen most clearly in FIGURE 6, and 24a is provided with circular aperture 41 having diametrically opposed radially extending notches 42a, 42b. The diameter of aperture 41 is slightly greater than the larger cross-sectional dimension of trip member portion 25b but is considerably less than the larger cross-sectional dimension of enlarged portion 25a. In the normal position of FIGURE 2, portion 25b extends through aperture 41 and through slot 39 in calibrating bushing 35. It is noted that slot 39, as best seen in FIGURE 3, is disposed on a diameter of bushing 35 and is rectangular with its smaller dimension being just slightly greater than the thickness of trip bar 25 and its larger dimension being slightly greater than the larger cross-sectional dimension of portion 25b but smaller than the larger cross-sectional dimension of enlarged portion 25a, for a reason which will hereinafter become apparent.

The angular position of calibrating bushing 35 is fixed by set scnews 52, 5,'3 which extend through arcuate slots 52a, 53a in calibrating bushing 35 and are received by threaded apertures in the end wall of ferrule 12. In the normal position of FIGURE 2 bushing 35 maintains enlarged portion 25a out of alignment with notches 42a, 42b. The passage of current through fusible element 14 causes bimetal 22 to heat and distort. Since end 32 of sleeve 21 is keyed within slot 33 of ferrule 13 the right end of bimetal 22 is effectively anchored to a fixed point of reference.

Thus, as bimetal 22 distorts tfhe left end thereof rotates causing latch sleeve 24 to rotate in the direction indicated by arrow B (FIGURE 3). When latch sleeve 24 rotates through angle A (FIGURE 3), notches 42a, 42h are aligned with enlarged portion 25a of trip bar 25. Now member 25 is free to move to the left with respect to FIGURE 2 with such movement taking place under the influence of spring 23. Leftward movement of trip member 25 is limited by the engagement of the left end of enlarged portion 25a with surface 36a of Calibrating bushing 35. Trip member 25 in moving to the left with respect to FIGURE 2 causes opening of a switch (not shown) as illustrated in the aforesaid Patent 2,982,834.

The angle A shown in FIGURE 3 represents the angular deflection of bimetal 22 from a cold position to a position corresponding to predetermined overload current conditions applied to device 10. That is, short circuit currents owing through device will cause fusible element 14 thereof to rupture resulting in a fusing of fulgarite 19 so as to cause circuit interruption in a short interval of time. This interval is so short that the energy absorbed by bimetal 22 will be insufficient to rotate latch sleeve 24 to a position for releasing trip member 25. The predetermined overload conditions necessary to cause release of trip member 25 are a combination of current and time with the combination being such that trip member 25 will be released before fusible element 14 can rupture. Y After trip member 25 is released and moves to the left with respect to FIGURE 2, the cooling of bimetal 22 tends to rotate latch sle'eve 24 in the direction opposite to that indicated by arrow B in FIGURE 3. However, slot 39 of calibrating bushing 35 retains trip member 25 in a predetermined angular position so that movement of latch sleeve 24 is restrained. Device 10 is reset by manually moving trip member 25 along its logitudinal axis to t'he .right at least until the position of FIGURE 2. This brings vend portion 25b in alignment with aperture 41 of latch sleeve 24 so that sleeve 24 is now free to rotate in a direction opposite to arrow B and thereby latch trip member 25 in the position shown in FIGURE 2.

Calibration of device 10 is achieved by loosening screws 52, 53 and moving calibrating bushing 35 to the particular angular position which requires the desired predetermined rotation of latch sleeve 24 in order to release trip member 25. Naturally, ferrules 12 and 13 are secured to housing 11 in a manner such that they are restrained against angular movement so that calibration is achieved through the positioning of slot 39 (FIGURE 3) relative to slot 33 (FIGURE 4).

In the embodiment of FIGURE 6 notches 42a, 42b in the end of latch sleeve 24 are rectangular in shape and are only slightly Vwider than the thickness of trip member 25. If the bimetal 22 is heated extremely rapidly it is conceivable that rotation of latch sleeve 24 will be so rapid that the alignment between notches 42a and 42b with enlarged portion 25a will be for such a short interval of time that spring 23 will be ineffective to project trip member 25 before notches 42a, 42b overshoot enlarged portion 25a. Further, heat stored in device 10 may cause the temperature of bimetal 22 to continue to rise excessively even after release of member 25. The distortion of bimetal 22 caused by this excessive heat is restrained through the engagement of latch sleeve 24 and trip member 25, bimetal 22 can be damaged or take a permanent set which would cause a change in calibration.

In order to prevent malfunctioning due to the conditions noted, the notch extensions of latch sleeve aperture 41 are enlarged as shown in FIGURE 8. More particularly, notches a, 60b have been opened up to a width considerably greater than the width of trip member 25. This added width assures that tripping will take place even after latch sleeve 24 overshoots and bimetal 22 will not be damaged or take on a permanent set even with a relatively great amount of excess heating.

Thus, the instant yinvention provides a fuse device which is capable of a longer useful life than conventional fuses in that the fusible element will be destroyed only under short circuit conditions. When an overload occurs the device can be reset. By utilizing a helically wound bimetal in the center bore of the fuse device the result is a simple and ,an inexpensive construction that can readily be fabricated to obtain and maintain desirable tripping characteristics. In addition, the switch used in conjunction with the fuse device of the instant invention does not have to be an accurate or sensitive mechanism since the trip member of the fuse device is capable of a long travel and can exert considerable tripping force.

Although there has been described a preferred embodiment of this novel invention many variations and modilications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows.

1. A device of the class described including a fusible element and an overload means operative responsive to the passage of predetermined overload current through said fusible element for a predetermined time interval, said current being insufficient to rupture said fusible element; said overload means including a first means, latch means normally maintaining said lirst means in a'lirst position, biasing means for moving said first means to a second position upon release of said latch means, and a bimetal operatively mounted wherein heat generated by current passing through said fusible element heats said bimetal causing disortion thereof; said latch means being released by said bimetal upon predetermined distortion thereof; said bimetal being a spiral having one end anchored; said latch means is rotated by said bimetal upon heating thereof; said bimetal formed about an axis, and said biasing means moving said rst means generally parallel to said axis upon release of said latch means.

2. A device as set forth in claim 1 in which the first means comprises an elongated member, said latch means normally blocking movement of said member, said'latch means having aperture means positionable in alignment with said member to permit the latter to move through said aperture to said second position, said latch means being unlatched when said aperture means is aligned with said member.

3. A device as set forth in claim 1 in which the first means comprises an elongated member having a first portion extending through an aperture in said latch means, said member having a second portion adjacent to said first portion, said aperture being insufficient in size to permit said second portion to pass therethrough, said latch means having notch means communicating with said aperture, said notch means in combination with said aperture being large enough to permit said second portion to pass therethrough, said latch means being unlatched when said notch means is aligned with said member.-

4. A device as set forth in claim 3 in which the notch means is enlarged with respect to said second portion to assure release of said latch means even upon excessive overload conditions and to permit overtravel of said latch means and thereby prevent damage to said bimetal even upon excessive heating thereof.

5. A device as set forth in claim 2 having a Calibrating means including an adjustable means operatively connected for positioning the member relative to the aperture means under normal operating conditions for the device.

6. A device of the class described including an insulating tubular housing formed about an axis, terminal means external of said housing, a fusible element and an overload `means disposed within said housing, said fusible element velectrically connected to said terminal means; said `overload means including a spiraled bimetal, a latch means secured to one end of said bimetal, said bimetal having its other end fixed with respect to said housing whereby heating of said bimetal is effective to move said latch means, a releasable member mounted for movement parallel to said axis, a coil spring, said latch means normally restraining said member in a first position against a biasing -force exerted by said spring against said member, said latch means being operable to a trip position for release of said member responsive to the passage of predetermined overload current through said fusible element for a predetermined time interval, said current being insufficient to rupture said fusible element; said member upon release thereof being moved to a second position through the action of said spring.

7. A device as set forth in claim 6 in which the bimetal and said housing are coaxial, said spring and said housing being coaxial, said member being elongated and being positioned on said axis, said latch means including a sleeve coaxial with said housing, said member having first and second axially aligned sections, said second section having a larger cross-sectional area than said rst section, an aperture in one end of said sleeve of a size sufficient to permit said first section to extend therethrough when said member is in said first position and of too small a size to permit passage of said second section, said aperture having an extension positionable in alignment with said second section and sufficient in size to permit said second section to pass therethrough, said extension and said second section being aligned when said latch means is in said trip position.

References Cited by the Examiner UNITED STATES PATENTS 2,200,309 5/ 1940 Siedle.

2,404,352 7/ 1946 Armstrong 200-116 2,982,834 5/1961 Edmunds 200-116 FOREIGN PATENTS 857 2/ 1931 Australia.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

1. A DEVICE OF THE CLASS DESCRIBED INCLUDING A FUSIBLE ELEMENT AND AN OVERLOAD MEANS OPERATIVE RESPONSIVE TO THE PASSAGE OF PREDETERMINED OVERLOAD CURRENT THROUGH SAID FUSIBLE ELEMENT FOR A PREDETERMINED TIME INTERVAL, SAID CURRENT BEING INSUFFICIENT TO RUPTURE SAID FUSIBLE ELEMENT; SAID OVERLOAD MEANS INCLUDING A FIRST MEANS, LATCH MEANS NORMALLY MAINTAINING SAID FIRST MEANS IN A FIRST POSITION, BIASING MEANS FOR MOVING SAID FIRST MEANS TO A SECOND POSITION UPON RELEASE OF SAID LATCH MEANS, AND A BIMETAL OPERATIVELY MOUNTED WHEREIN HEAT GENERATED BY CURRENT PASSING THROUGH SAID FUSIBLE ELEMENT HEATS SAID BIMETAL CAUSING DISTORTION THEREOF; SAID LATCH MEANS BEING RELEASED BY SAID BIMETAL UPON PREDETERMINED DISTORTION THEREOF; SAID BIMETAL BEING A SPIRAL HAVING ONE END ANCHORED; SAID LATCH MEANS IS ROTATED BY SAID BIMETAL UPON HEATING THEREOF; SAID BIMETAL FORMED ABOUT AN AXIS, AND SAID BIASING MEANS MOVING SAID FIRST MEANS GENERALLY PARALLEL TO SAID AXIS UPON RELEASE OF SAID LATCH MEANS. 